1. Field of the Invention
The present invention concerns a linear motor whose moving part has a stator formed of several pieces assembled in the longitudinal direction of this moving part.
2. Discussion of Related Art
A linear motor stator, segmented into several pieces or parts that are assembled once these pieces or parts have been produced, has several advantages.
First, it is possible to define a basic piece of elemental length for the body of the stator. During the final assembly of the stator, it is possibly to vary its length in accordance with the type of linear motor built or in accordance with the application for which it is intended, by assembling a variable number of prefabricated basic pieces. Secondly, a structure of this type makes it possible to produce the two end parts or teeth separately from the body of the stator, then assemble them to this body in a subsequent step.
A linear motor whose moving part is formed by a stator comprising a body and end teeth assembled to this body is known from U.S. Pat. No. 6,713,899, the entire contents of which are incorporated herein by reference. The end parts or teeth have an inverted L-shape, with a rectangular end projection that is inserted into an upper recess of the stator, this recess being machined into the upper surface of this body. Thus, the end tooth is attached only at its upper end. The rigidity of such an assembly is not properly assured. Because the end tooth is only attached at its upper end, vibrations can be generated in the lower part located near the motor's permanent magnets. In fact, since the contact between the lateral surfaces at the joint between the end tooth and the body is not maintained by a specific fastening, these lateral surfaces can separate from one another either dynamically, generating vibrations, or statically, creating an air gap between the end part and the body of the stator.
A linear motor with a segmented stator that makes it possible to produce a relatively long stator is known from the document DE 3110339. According to this document, a long stator is produced by assembling elemental stator pieces that define a functional stator having a given overall length. Thus, the elemental stator piece includes a plurality of teeth defining slots for windings and two end teeth whose lower surface defines a plane that is inclined relative to a horizontal direction corresponding to the direction of movement of the stator. The elemental stator pieces are assembled by distinct fastening elements disposed in the upper part of the stator and inserted on either side of the joint between two stator parts in T-shaped recesses produced in the upper surfaces of the two respective stator pieces. These structures for assembly have the same drawbacks as those described in connection with the preceding document. In essence, the stator pieces are joined only by fastenings disposed on the upper surfaces of these stator pieces. Thus, neither a separation of these two pieces nor vibrations can be ruled out. The dynamic behavior of the stator can therefore be disturbed, which is harmful in several applications wherein the moving part is subject to large accelerations. The segmented stator proposed in this document has another major drawback in that the tooth formed at the level of the joint between two stator pieces does not have a flat and horizontal lower surface like that of the other teeth. This increases the reluctance effect of the stator and reduces its efficiency.